Congrats on your maturity at a such a young age.   

@Polat CaglayanI've never seen a formula but here is a general rule of thumb for multifamily:The class of an apartment refers to the quality of the building, which can be determined by a number of factors, including age, location, and condition: Class A: These are the highest quality apartments, typically built within the last 15 years.

Be careful not to place your identity in your age/success in RE.

Congratulations on building such an impressive portfolio at such a young age and achieving so many successes!

I've been at this a while and have over 70% equity in my combined portfolio, and I'm over 50 years of age, so I don't look at creative financing options. 

Items like a missing doorbell or blinds may fall into wear-and-tear depending on their age.

For (2), as properties age the rents you command decrease. 

My question is: could the current tenant (age 59) remain in the property if she becomes eligible for Section 8 assistance?

There is so much to learn between the ages of 18-22. 

I've tried a couple - truepeoplesearch, white-ages, property radar, leadsherpa, batch leads...Some services are better than others, but it is a numbers game and you also can cross check between different platforms.